Focus MK3.5 Sound System Upgrades

Ok so my mk3.5 has the Sony sound system upgrade. With Max bass, 2/3rds boost on midrange and +1 treble it sounds almost how I'd like. I listen to music via Android auto as it allows a much less grainy, delayed and compression-artifacty listening experience, on between 8 and up to 18 volume at most. I listen to mostly pop music (although nothing too tappy and rappy) so I like bass, but don't want to lose the rest of the tune to thudding or the effect that sounds like when you talk through a fan. I don't play it too loud also because I'd look like proper racer-boy and ASB-type, you know, the ones in the lowered, tinted, black 2013 3-series with the window down. I want deep and rumbly bass that doesn't make any other part of the car make noise (ie rattles). A few examples:

'How Will I Know' - Whitney Houston + Clean Bandit, '7 Rings' - Ariana Grande, 'Don't Be Shy' - Tiesto + KAROL G, 'I'll Be There' - Jess Glynne, 'Levitating (feat. DaBaby)' - Dua Lipa, 'New Rules' - Dua Lipa, and 'I Would Like' by Zara Larsson.

I want to know what upgrades people have done to their systems, from basic to professional, and what I could do to mine. 

My plan was to swap the OEM woofers and tweeters for branded ones as I'm led to believe the Sony system only has the extra speakers and better amp, not better drivers. Also to lather dynamat on the inside of the door and secure anything loose as I often hear rattles from the door cards. I've heard of people putting amps from other models (ie a Kuga amp) in their focus, if that checks out then I'd definitely be up for it. Some have recommended that I unplug the centre dash speaker to enhance quality. I'm happy to give it a go but I am fond of the elevated and front-firing effect it has.

Would I be looking at replacing the crossovers? If wiring speakers in that don't have the plugs the OEM ones have and come with crossovers? I want to avoid too much rewiring, but it's something I can tackle.

What brands should I look out for? I fitted some JBLs in my last car and they were good actually, but I'm aware there's a lot of choice.

Thanks!